661861840 has 40 divisors (see below), whose sum is σ = 1539901440. Its totient is φ = 264560256.

The previous prime is 661861813. The next prime is 661861853. The reversal of 661861840 is 48168166.

It is a tau number, because it is divible by the number of its divisors (40).

It is a super-2 number, since 2×661861840² = 876122190496371200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (40).

It is a junction number, because it is equal to n+sod(n) for n = 661861793 and 661861802.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 213421 + ... + 216499.

It is an arithmetic number, because the mean of its divisors is an integer number (38497536).

Almost surely, 2^661861840 is an apocalyptic number.

It is an amenable number.

661861840 is an abundant number, since it is smaller than the sum of its proper divisors (878039600).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

661861840 is a wasteful number, since it uses less digits than its factorization.

661861840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5779 (or 5773 counting only the distinct ones).

The product of its (nonzero) digits is 55296, while the sum is 40.

The square root of 661861840 is about 25726.6756499941. The cubic root of 661861840 is about 871.4767011464.

The spelling of 661861840 in words is "six hundred sixty-one million, eight hundred sixty-one thousand, eight hundred forty".